Since wireless communication has no physical line connecting a transmitter to a receiver, it is difficult to understand intuitively which devices are connected. The procedure for setting up a connection is also complex. Wired communication, on the other hand, uses a visible signal transmission path, allowing an intuitive operation to connect devices with a cable. However, wired communication has the disadvantages of a confusing layout as more cables are laid and of the continuous need to disconnect and reconnect cables when multiple devices communicate with each other.
To address these issues, methods have been proposed to capitalize on the advantages of wired communication, which allows clear selection of a communication partner through physical contact, while allowing communication without laying new cables. These methods overlay high frequency signals on existing transmission lines, so that when devices are separated, communication is not performed, whereas when another device is touching, communication is performed with the other device.
For example, methods have been proposed for communication between devices connected to a transmission line network by overlaying high frequency signals on existing transmission lines and for communication between devices in contact with a human body by overlaying high frequency signals on the human body, using the human body as a communication medium (for example, see patent literature (PTL) 1 and PTL 2).